Technical Field
Aspects of the embodiments generally relate to roller shades, and more particularly to systems, methods, and modes for counterbalancing a roller shade with pretensioned spring and method for pretensioning the spring to lower the torque load on the motor of the roller shade throughout the rolling up or rolling down cycles of the roller shade.
Background Art
Motorized roller shades provide a convenient one-touch control solution for screening windows, doors, or the like, to achieve privacy and thermal effects. A motorized roller shade typically includes a rectangular shade material attached at one end to a cylindrical rotating tube, called a roller tube, and at an opposite end to a hem bar. The shade material is wrapped around the roller tube. An electric motor, either mounted inside the roller tube or externally coupled to the roller tube, rotates the roller tube to unravel the shade material to cover a window. To uncover the window, however, a lot of torque and motor power are required to initially lift the entire weight of the shade material and the hem bar. This is in particular detrimental to battery operated motors as rolling up the shade quickly drains the battery.
Various methods exist for counterbalancing roller shades using springs mounted inside the roller tubes in an effort to reduce torque requirements on shade motors. As the roller shade is unraveled, tension builds up in the spring. The tension is released when the roller shade is rolled up, thereby assisting the motor in lifting the shade material. One approach uses a conventional torsion spring comprising a plurality of coils. As a torsion spring is wound up, it builds up torque. When the torsion spring is let go, the amount of torque exerted by the torsion spring progressively reduces in a linear fashion as the torsion spring winds down. FIG. 1A shows a diagram 100 representing the performance of a conventional torsion spring in assisting rolling up an exemplary sized roller shade. Line 105 represents the torque profile necessary to roll up an exemplary sized roller shade from a rolled down position, when the shade material is fully unraveled, up to a rolled up position, when the shade material is fully wrapped about the roller tube. Initially, more torque is required to lift the entire weight of the fully unraveled shade material and the hem bar as represented by maximum torque (Tmax) value 102. As the roller tube turns, the shade material wraps around the roller tube, resulting in less shade material hanging from the roller tube. Accordingly, as the roller tube keeps turning, less torque is required to lift the weight of the remaining shade material until a minimum torque (Tmin) value 103 is reached. Line 106 represents the torque exerted by the torsion spring during the roller shade travel. As shown, the torsion spring torque 106 decreases at a slope in a linear fashion to a zero value as the torsion spring winds down.
Currently, a torsion spring is chosen with a torque 106 that approaches the Tmax value 102 required to lift the shade material and the hem bar. The resulting torque, shown by line 108 in the figure, required to be exerted by the motor to roll up the roller shade is equal to the difference between the torque of the roller shade 105 and the spring torque 106. FIG. 1B shows a diagram 101 representing the resulting power 110 required of the motor to roll up the shade. As the roller shade begins to roll up from a fully unrolled position, the torsion spring releases its built up torsion energy. Then its energy progressively diminishes as the roller shade continues to roll up. At the end of the rolling up cycle, the torsion spring unravels back to zero torsion assistance. Thus, a conventional torsion spring assists the motor significantly more when the roller shade begins to roll up than during the remainder of the rolling up cycle. In the example of FIGS. 1A and 1B, initially about 0.1 N m of torque and less than 1 W of power are required to lift up the roller shade. That number climbs up to above 0.8 N m of torque and above 6 W of power at the end of the roll up cycle. Thus, while the conventional torsion spring decreases the amount of torque required to roll up the roller shade in the beginning, the amount of torque and power required to finish rolling up the roller shade remains quiet high.
Counterbalancing systems exist that pretension the spring in the roller shade to further assist in rolling up the roller shade. One such system allows pretensioning the spring during the installation of the roller shade. However, field pretensioning is often done incorrectly, leaving the customer unsatisfied with the performance of the product. Therefore, it is desired to have a factory settable pretension of a spring. Other systems exist that allow factory settable pretensioning by providing means that temporary hold the pretension until the roller shade is installed. Thereafter, the pretension is held by the weight of the shade material. However, this preset pretension often dissipates during the continual operation of the shade, when the shade is knocked down or hit accidentally, or when the shade needs to be removed and reinstalled. Other systems required complex field adjustment and complicated motorized pretensioning.
Therefore, a need has arisen for systems, methods, and modes for counterbalancing a roller shade with a pretensioned spring and method for pretensioning the spring to lower the torque load on the motor of the roller shade throughout the rolling up or rolling down cycles of the roller shade. Additionally, a need has arisen for systems, methods, and modes for counterbalancing a roller shade with pretensioned spring that can be pretensioned at the factory to a preset amount and which locks and continuously maintains the pretension.